The draft is a vessel's waterline, which equals the vertical distance between the keel and the water surface (depth). Inclination in the breadth direction of the vessel (heel) causes draft difference between portside and starboard. The draft difference can be obtained by reading draft marks which are placed on both sides of the vessel. Reading the draft on the shore side is easy, while on the sea side is difficult. As substitute for reading the marks, there is a well-known instrument for easily measuring draft difference on the deck (Patent Literature 1). Based on measurements obtained by using the instrument, it is possible to know the degree of inclination in the breadth direction of the vessel and to calculate an angle of inclination.
The principle of measuring draft difference between both sides on the deck is the same as those disclosed in Patent Literatures 2-7. The principle is briefly described as follows. When two reservoirs containing liquid to be used for measuring, such as water or the like, (hereinafter referred to as “measuring liquid”) are placed apart from each other and connected through a hose, etc., both liquid levels are even. Then calculating the difference in the height from the surface on which each reservoir is placed to the liquid level represents the elevation difference in two places. The instruments disclosed in Patent Literatures 2-7 are for onshore use but not for measuring draft difference between both sides of a vessel.
The inclination measuring instrument of Patent Literature 1 is provided with two tubular liquid-level gauges corresponding to the two reservoirs in the principal and a long transparent flexible tube (instead of this term in Patent Literature 1, “communicating hose” is used herein) for communicating the gauges at their lower ends. The inclination measuring instrument is filled with liquid not generating air bubbles. When used in a large vessel, the length of the hose reaches tens of meters. When not in use, the hose is wound on a drum in duplex with the central portion of the hose in the length direction as starting end.
Patent Literature 1 describes the communicating hose as being “one” hose; however, this is no more than a principled description. The hose is actually arranged as shown in FIG. 7.
FIG. 7 shows conventional art for winding the communicating hose on a drum in duplex in a schematic view of only main parts of a drum 100.
The drum 100 is provided with a spindle 101, a pair of disks 102 at both ends of the spindle, and a handgrip 103 at one side. The spindle 101 has a closed hollow 104 inside and is provided with a forked pipe 105 projecting from the outer periphery. The base end of forked pipe 105 opens into the hollow 104. The other end of the forked pipe 105 diverges into joints 106a and 106b. One end of a left hose 107a is fixed to one of joints 106a, and one end of a right hose 107b is fixed to the other joint 106b. The other end of left hose 107a is connected to the tubular liquid-level gauge (not shown) installed on the portside, and the other end of right hose 107b is connected to the tubular liquid-level gauge (not shown) installed on the starboard.
The communicating hose used in conventional inclination measuring instruments such as Patent Literature 1 comprises left hose 107a and right hose 107b that is made by severing one hose at its midpoint. The two independent hoses communicate with each other through the forked pipe 105 and the hollow 104 of the spindle 101.